1. Field of the Invention
The present invention relates to a zinc oxide based semiconductor device and a method for producing same.
2. Description of the Related Art
Zinc oxide (ZnO) is a direct band gap semiconductor having a band gap energy of 3.37 eV at room temperature and holds promise as a material for use in optical devices in the blue-ultraviolet region. In particular, zinc oxide possesses physical properties that are especially suitable for semiconductor light-emitting devices; i.e., an exciton binding energy of 60 meV and a refractive index (n) of 2.0. Zinc oxide can be used not only in light-emitting devices and light-receiving devices, but also in surface acoustic wave (SAW) devices, piezoelectric devices, and the like. Furthermore, zinc oxide is inexpensive in terms of raw materials and has no adverse effects on the environment or the human body.
When semiconductor devices are cut from a wafer on which is formed a semiconductor crystal layer that constitutes the semiconductor device, device dividing grooves or scribes are formed on the wafer, and the devices are then separated using a knife edge or the like. For example, crystals having a zinc blende structure such as GaAs (gallium arsenide)-based compound semiconductors or InP (indium phosphide)-based compound semiconductors have a good cleavage property on the (110) face and therefore present little problem when semiconductor devices are cut from a wafer. However, wafers on which a nitride semiconductor layer having a wurtzite structure is formed have poor cleavage properties and are therefore likely to crack or exhibit other cutting defects (e.g., refer to Japanese Patent No. 2780618 (patent document 1), page 2, FIG. 1 and Japanese Patent No. 2861991 (patent document 2), page 2, FIG. 1).
For example, patent document 2 discloses a scribe on a wafer in which a nitride semiconductor layer is formed on a sapphire substrate, wherein dividing grooves are formed to a depth at which a part of the sapphire substrate is removed in order to prevent the occurrence of chip defects that cause the cutting line to curve, thereby preventing a straight cut. However, zinc oxide (ZnO)-based compound semiconductor crystals, which have the same hexagonal wurtzite structure as this nitride semiconductor albeit with different characteristics and physical properties, have not been sufficiently investigated in terms of the problems that occur during the device separation step.